finagle-thrift: Expand ThriftRichClient#params

Problem
ThriftRichClient makes `param` protected when it's not in the variants of `Stack.Parameterized`
we've created. This makes it tough when sharing config between Thrift/ThriftMux to access
client params since they share `ThriftRichClient` as an interface mixin.

Solution / Result:
`ThriftRichClient` already has StackClient as a self-type meaning the params attribute
already exists. Lets just remove it altogether in ThriftRichClient

JIRA Issues: CSL-11746

Differential Revision: https://phabricator.twitter.biz/D837051

finagle-thrift/src/main/scala/com/twitter/finagle/thrift/ThriftRichClient.scala

@@ -9,7 +9,6 @@ import com.twitter.finagle.util.Showable
 import com.twitter.finagle.Name
 import com.twitter.finagle.Resolver
 import com.twitter.finagle.Service
-import com.twitter.finagle.Stack
 import com.twitter.finagle.Thrift
 import org.apache.thrift.protocol.TProtocolFactory
 import scala.reflect.ClassTag
@@ -126,14 +125,6 @@ trait ThriftRichClient { self: StackBasedClient[ThriftClientRequest, Array[Byte]
   protected val defaultClientName: String
   protected def stats: StatsReceiver = ClientStatsReceiver
 
-  /**
-   * The `Stack.Params` to be used by this client.
-   *
-   * Both [[defaultClientName]] and [[stats]] predate [[Stack.Params]]
-   * and as such are implemented separately.
-   */
-  protected def params: Stack.Params
-
   /**
    * $clientUse
    */